The present invention relates to a deflection yoke installed in an in-line color television picture tube.
In a picture display apparatus using an in-line color television picture tube equipped with three electron guns, it is necessary to converge the three electron beams produced from the three electron guns on a screen surface. To this end, a conventional convergence method uses a self-convergence type deflection yoke. The self-convergence type deflection yoke generally comprises a pair of upper and lower saddle type horizontal deflection coils and a pair of right and left saddle type vertical deflection coils to realize a desirable convergence performance.
However, a practical problem arises when the deflection yokes are mass produced. Convergence errors may occur due to dispersion in the performance of mass-produced saddle coils. To correct such convergence errors, an adequate adjustment is performed by attaching a magnetic piece to an appropriate portion of the coil or using a correction circuit.
FIGS. 13A and 13B show typical convergence errors caused by the dispersion of the horizontal deflection field. FIG. 13A shows a pincushion type convergence error of an X (i.e., horizontal) axis. The pincushion type convergence error appears when the pincushion of the horizontal deflection field is excessively strong. FIG. 13B is a barrel type convergence error of the X axis that is found when the pincushion of the horizontal deflection field is excessively weak. In FIGS. 13A and 13B, each solid line represents a vertical bright line of red and each dotted line represents a vertical bright line of blue. The convergence errors shown in FIGS. 13A and 13B are generally referred to as xe2x80x9cXH convergence errors.xe2x80x9d
Unexamined Japanese Patent Application No. Kokai 2-215031, published in 1990, discloses a conventional deflection yoke used for collecting this kind of XH convergence error. As shown in FIG. 14, this conventional deflection yoke comprises a horizontal deflection coil 1 consisting of a main coil 1a and an auxiliary coil 1b. The auxiliary coil 1b serves as a winding introductory part or a winding terminal part of the main coil 1a. A variable inductance coil 2 is connected in parallel with the auxiliary coil 1b. This arrangement requires intermediate taps 3 provided in the horizontal deflection coil 1.
According to this conventional arrangement, the variable inductance coil 2 functions as a bypass circuit which has the capability of controlling a horizontal deflection current flowing across the auxiliary coil 1b connected in parallel with the variable inductance coil 2. This makes it possible to adjust a magnetic field generated at the horizontal deflection coil. With this arrangement, it becomes possible to correct the XH convergence error shown in FIGS. 13A and 13B.
FIG. 15 is a plan view showing a deflection yoke seen from an outlet (i.e., larger-diameter) side of electron beam. A funnel or bell-mouthed separator 4 accommodates a pair of upper and lower horizontal deflection coils 1 along an inner surface thereof. Each horizontal deflection coil 1 is formed into a saddle shape with a window 5. The upper and lower horizontal deflection coils 1 are opposed each other via a butt portion 6.
The auxiliary coil 1b shown in FIG. 14 may be disposed at a region A adjacent to the window 5 corresponding to the inner peripheral portion of the horizontal deflection coil 1 shown in FIG. 15 to decrease the horizontal deflection current in the region A. This arrangement enhances the pincushion of the horizontal deflection field. It becomes possible to correct the barrel convergence error shown in FIG. 13B.
However, controlling the current of a limited section adjacent to the window 5 may cause a difference between a convergence variation on the X-axis of the screen and a convergence variation at the corner of the screen. FIG. 16 shows a convergence error still remaining even after the XH convergence error is corrected according to this conventional correcting method.
On the other hand, the auxiliary coil 1b shown in FIG. 14 may be disposed at a region B adjacent to the outer peripheral portion of the horizontal deflection coil 1 shown in FIG. 15 to control the horizontal deflection current in the region B. However, even in this arrangement, the convergence error appears as shown in FIG. 16.
An object of the present invention is to provide a deflection yoke capable of adequately correcting the XH convergence error.
Another object of the present invention is to provide a deflection yoke simple when it is assembled.
Another object of the present invention is to provide a winding method of deflection coil.
Another object of the present invention is to provide a deflection yoke having a sufficiently enlarged variable range in the inductance for adequately correcting the XH convergence error, without increasing the turn number of the coil or the length of the core unnecessarily.
In order to accomplish the above and other related objects, a first aspect of the present invention provides a deflection yoke comprising at least one saddle type horizontal deflection coil, characterized in that each horizontal deflection coil has at least three regions extending from a winding introductory part to a winding terminal part, and a control device is provided for controlling a horizontal deflection current flowing across a predetermined intermediate region of the horizontal deflection coil.
Preferably, the control device is a variable inductance coil connected in parallel with the intermediate region of the horizontal deflection coil.
A second aspect of the present invention provides a deflection yoke comprising a pair of saddle type horizontal deflection coils, wherein a pair of auxiliary deflection coils are connected to the horizontal deflection coils and disposed in a region between an inner peripheral portion of the horizontal deflection coils adjacent and a yoke window and an outer peripheral portion of the horizontal deflection coils.
Preferably, the auxiliary deflection coils overlap with the horizontal deflection coils. The deflection yoke may further comprises a control device for controlling the horizontal deflection current flowing across the auxiliary deflection coils. Preferably, the control device is a variable inductance coil connected in parallel with the auxiliary deflection coils. Furthermore, it is preferable that an electric wire used for the auxiliary deflection coils is differentiated in at least one of color, wire diameter and strand pitch from an electric wire used for the horizontal deflection coils.
A third aspect of the present invention provides a method of winding a horizontal deflection coil installed in a deflection yoke, comprising a step of winding the horizontal deflection coil in a cylindrical fashion from one end to the other end, and further comprising a step of winding an auxiliary deflection coil in addition to the horizontal deflection coil in an intermediate region between the one end and the other end, the auxiliary deflection coil being connected to the horizontal defection coil.
Preferably, the auxiliary deflection coil is wound together with the horizontal deflection coil, or wound independently of the horizontal deflection coil. It is also preferable that the electric wire used for the auxiliary deflection coil is differentiated in at least one of color, wire diameter and strand pitch from the electric wire used for the horizontal deflection coil.
A fourth aspect of the present invention provides a variable inductance coil comprising a bobbin having a hollow space, a first core installed in the hollow space of the bobbin and shiftable in a longitudinal direction of the hollow space, a coil connected in parallel with an auxiliary deflection coil and wound around the bobbin, and a second core having an end surface larger in area than an end surface of the first core, the second core being disposed adjacent to an end portion of the hollow space.
Preferably, the second coil is independent of or integral with the first core. The variable inductance coil may be incorporated in a deflection yoke comprising an auxiliary deflection coil connected to a horizontal deflection coil and disposed in the region between the window corresponding to the inner peripheral portion of the horizontal deflection coil and the outer peripheral portion of the horizontal deflection coil. The variable inductance coil controls the horizontal deflection current flowing across the auxiliary deflection coil.